1. Field of the Invention
The invention relates to a shift controller and a shift control method for an automatic transmission mechanism configured to be capable of controlling an engine revolution speed by controlling a gear ratio of the automatic transmission mechanism.
2. Description of the Related Art
In a driven mode in which the engine is driven by power inputted from wheels, for example, when a vehicle decelerates, friction in the engine and a mechanical hydraulic pump driven by the engine becomes a load and the so-called engine brake force is generated. However, of this engine brake force, a load generated as the mechanical hydraulic pump is driven can make the engine brake force too large. Japanese Patent Application Publication No. 3-134368 (JP-A-3-134368) describes an example of configuration designed to reduce the engine brake force. In the configuration described in JP-A-3-134368, an electrically driven high-pressure oil pump that generates a relatively high hydraulic pressure is used to supply hydraulic pressure to a pulley of a V-belt continuously variable transmission mechanism that requires a relatively high hydraulic power, whereas a mechanical low-pressure oil pump that is driven by an engine is used to supply pressurized oil to a hydraulic clutch and a fluid transmission unit that may operate at a relatively low hydraulic pressure, but require pressurized oil at a high flow rate.
Japanese Patent Application Publication No. 2004-316832 (JP-A-2004-316832) describes an invention relating to a configuration having a line pressure circuit system (high hydraulic pressure circuit) into which a relatively high hydraulic pressure is supplied and another circuit system (low hydraulic pressure circuit) that uses a hydraulic pressure of a drain from the line pressure circuit system as a hydraulic pressure source, wherein a discharge pressure of an oil pump driven by the engine is supplied to the line pressure circuit system and a hydraulic pressure reduced by a regulator valve is supplied to the other circuit system (low hydraulic pressure system). Furthermore, Japanese Patent Application Publication No. 7-280080 (JP-A-7-280080) describes a configuration in which an oil pump is driven when upshifting is performed that reduces the gear ratio, and the engine revolution speed is rapidly reduced by the drive resistance of the oil pump.
According to the invention disclosed in JP-A-3-134368, oil pumps of two types, namely, a low-pressure oil pump and a high-pressure oil pump, are provided. Therefore, a hydraulic pressure suitable for a torque converter, a clutch, and a continuously variable transmission mechanism can be supplied, the drive torque of the oil pump as a whole can be reduced, and the power loss or hydraulic pressure deficiency can be prevented or inhibited. However, in the configuration described in JP-A-3-134368, when extra hydraulic pressure on the low hydraulic pressure side is regenerated to an accumulator located on the high hydraulic pressure circuit side, an engine brake force is increased by a (drive) load of the mechanical low-pressure oil pump driven by the engine, for example, when the vehicle is decelerated.
According to the inventions disclosed in JP-A-2004-316832 and JP-A-7-280080, the power inputted from the wheels, for example, when the vehicle is decelerated, is received by an engine or an oil pump driven by the engine. Therefore, the engine brake force is increased by an oil pump load, an un-planned deceleration feeling is created, and drivability can be degraded.